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Viscosity of Polymer Solutions

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Viscosity of Polymer Solutions Abstract: By experiment, it was found that the approximate size of a polymer molecule in solution was that of a radius of 9.77?10�8 � 0.60?10�8 m. The polymer used was Polyethylene Oxides, or PEO. This value was obtained by measuring the time taken or a sphere to fall a known distance, within a polymer solution of known concentration. From this result, using theory, it was concluded that the conformation of the polymer molecule in solution was that of a loose, irregular coil. The experiment also verified Einstein's 1908 law linking viscosity of a fluid containing a dispersion of small solid spheres, for dilute solutions, ? = ??( 1 + k c ) by plotting a graph of ln(viscosity) against ln(concentration). The law linking viscosity to concentration for larger concentrations, ? = b c was also verified using the same graph. Both graphs were straight lines that crossed at the point where all the polymer molecules in the solution were just touching. This point was used to determine the radius of the molecules Introduction: The aims of the experiment were: 1) To obtain a value for the size of a single polymer molecule in solution and to therefore deduce its conformation. 2) To show and measure the dependence of polymer solution viscosity on concentration. Viscosity is the property of a fluid that causes a drag force when a solid moves through the fluid. ...read more.


4) As the solution became less viscous, the spheres began to fall more quickly and soon became to fast to time accurately. At each different concentration I tried dropping very small, clear spheres into the solution in the same way as the larger, black spheres. These balls did not fall sufficiently enough to measure until the solution was at a concentration of 0.235g per 100ml. For this concentration, and the next concentration to be tested, I timed both the black and clear spheres. After that point, I timed only the clear. The overlap between the two sets of results gave me a conversion factor between measurements. Diagram: Results: Sphere Concentration / g per 100ml Distance fallen / ml Time 1 Time 2 Time 3 Average Time Black 0.625 5 14.97 15.18 14.91 15.02 Black 0.469 5 6.78 6.22 6.25 6.42 Black 0.352 10 2.19 2.32 2.38 2.30 Black 0.235 20 1.50 1.65 1.84 1.66 Clear 0.235 2 20.75 16.63 17.91 18.43 Black 0.156 20 0.96 0.97 0.94 0.96 Clear 0.156 2 11.02 8.19 10.56 9.95 Clear 0.104 5 8.28 8.84 8.30 8.47 Clear 0.069 5 6.18 6.72 6.69 6.53 Clear 0.046 5 3.78 4.06 4.65 4.16 Clear 0.031 10 3.94 4.10 4.59 4.21 The average time for a 5ml drop for each result was then calculated, as well as the ratio between the two types of sphere. ...read more.


90 000 = 3.6?10�5m Too big * Molecule as tight ball: diameter = monomer length ? 3V90 000 = 1.8 ?10�8m Too small * Molecule as loose, irregular coil: r = a VN V6 = 4.90?10�8m Similar to experimental result. Therefore, polymer in solution likely to be a loose, irregular coil. Conclusion My experiment was successful and I obtained a good result. I verified that viscosity obeys the two laws stated previously. A problem with my experiment was that the qualitative errors stated were too small; the theorized answer lay outside my error margins. A large error in the experiment was with concentration, the solution repeatedly was diluted and any errors increased progressively over time. To make these errors smaller, fresh solution should have been used and diluted each time. To get a better result, a wider range of different sized spheres could have been used. This would have given more accurate conversion factors. In my experiment, large errors resulted from using the small clear spheres. These spheres were fairly non-uniform in both size and shape and were easily carried by currents resulting from stirring of the solution. From this experiment, I leant that the size of a polymer molecule in solution is 9.77?10�8 � 0.60?10�8 m, and that the shape of this molecule is that of a loose, irregular coil. I also learnt that polymer molecules in solution obey the laws ? = ??( 1 + k c ) and ? = b c. ?? ?? ?? ?? Clare Mawdsley ...read more.

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